Lubricating oil thickened to a grease with asphaltene absorbed clay



United States Patent LUBRICATING OIL THICKENED TO A GREASE WITHASPHALTENE ABSORBED CLAY Donald E. Loeffler, Walnut Creek, Calif.,assignor to Shell 011 Company, a corporation of Delaware No Drawing.Filed Apr. 13, 1959, Ser. No. 805,715

5 Claims. (Cl. 252-28) This invention relates to an improvement ingrease compositions. More particularly, it relates to greasecompositions having improved water resistance and resistance todeterioration in the presence of ionizing radiation.

Grease compositions normally comprise a gelling agent dispersed incolloidal form in a lubricating oil base. Many types of gelling agentsand of oil bases have been investigated. and utilized. The most widelyemployed greases are gelled with soaps of high molecular weight fattyacids and mineral lubricants are the most generally utilized oil base.However, greases gelled with soaps have certain inherent disadvantageswhich cannot be overcome by the use of additives or by other means thansubstitution of-the soaps. The soap-base greases, for example, exhibitsoftening points at relatively moderate temperatures which are normallysubstantially below the decomposition temperature of either the soap orof the oil. This is due in large part to the relatively low meltingpoint of the soap fibers dispersed in the oil.

The problem of softening or even fiuidizing at relatively lowtemperatures has been cured in a substantial measure by substituting forthe soaps gelling agents which may be broadly referred to as microgels.These comprise a large variety of colloidal substances which are eitherinorganic colloids or are organic derivatives of these colloids. Typicalmaterials include silica, clays and the so-called onium clays as well assurface esterified colloids, such as butylated silica and the like.Unless the colloids are protected by the presence of hydrophobingagentsor surface treatment, the greases prepared therefrom exhibit watersensitivity which limits their field of use. The onium clays and thesurface esterified silica are waterproofed by surface treatments. Inthese cases the ester groups or the onium radicals perform ahydrophobing function, providing the colloids with an oleophilic surfacewhich enables them to maintain their grease structure even in thepresence of water.

The hydrophobic surfactants normally utilized for improving the waterresistance of greases gelled with inorganic colloids includeparticularly the cationic surfactants which may be amines and aminoamides, preferably aliphatic in character and of relatively highmolecular weight. While these improve the Water resistance of thecolloidal gelled greases containing them, they do not prevent (in fact,they even accelerate) sensitivity of ice 2 the grease is made up of thecost of the individual ingredients. Consequently, any reduction in thecost of an essential ingredient correspondingly lowers the cost of thetotal grease composition and thereby improves the possible applicabilityof the grease to additional indus trial usage. Ordinarily, the mostexpensive ingredient utilized in the microgel grease systems is thehydrophobing additive, since the gelling agent and the lubricant are inmost instances relatively less costly. Th ehydrophobic surfactants areutilized for the sole reason that they are essential for the promotionof Water resistance of the 'grease compositions containing them.

It is an object of the present invention to improve greasecompositions.It is another object of the invention to improve the resistance ofgrease compositions to degradation in the presence of ionizingradiation. It is a further object of the invention to provide microgelgrease compositions exhibiting not only high water resistance but alsoresistance to degradation caused by ionizing radiation. It is a furtherobject to provide the foregoing benefits while at the same timedecreasing the cost of the grease compositions. Other objects Willbecomeapparent in the following description of the invention.

Now, in accordance with the present invention, grease composition areprovided which exhibit excellent water resistance, have no droppingpoint and are stable in the presence of ionizing radiation while at thesame time the cost of the composition is reduced. These compositionscomprise a lubricating oil gelled to a grease consistency with aninorganic colloidal gelling agent, the agent bearing on the surface ofthe colloidally dispersed particles asphaltenes, as more fully definedhereinafter, in an of the grease to ionizing radiation. Thus, when manygreases are subjected to the influence of ionizing radiation, theyexhibit their sensitivity in one of two directions. First, many greaseswill fiuidize and lose their grease" structure. On the other hand, othergreases will become rubbery in texture and lose their lubricatingpropertiesflfl In either case'an unsatisfactory resultlhas beenobtained. In the case of soap-base greases it is the universalexperience that such greases fiuidize upon exposure to ionizingradiation. a

i always be considered i cations due to their cost. Of course, the totalcost of amount sufficient to provide the grease composition with waterresistance and stability against degradation due to ionizing radiation.More particularly, preferred compositions comprise mineral oil brightstocks gelled to a grease consistency with colloidally dispersed clay,the clay bearing 25-100% by weight (based on. the clay) of oxidizedasphaltenes.

, While the asphaltenes which are employed for the present purpose maybe naturally occurring components obtained from petroleum residues asmore fully described hereinafter, much better results are obtained ifthey have been subjected to an oxidizing treatment, preferably airblowing or other oxidation by means of oxygen-contain-. ing gas.

The term asphaltenes is defined in Abraham, Asphalts and AlliedSubstances, Fifth Edition, pages 1165-6, as being the non-mineralconstituents remaining insoluble in petroleum naphtha, thusdifferentiating them from the maltenes (petrolenes) which dissolve inthe same medium and under the same conditions. As the test is run atroom temperature (6 5-75 R), this latter constitutes a part of thedefinition. A still further limitation is the proportion of petroleumnaphtha employed for the purpose of causing separation. I According tothe standardized method, 50 volumes of petroleum naphtha areemployed,;the test temperature normally being ambient room temperature.While this standard procedure defines the term, it will be understoodthat the asphaltic fraction insoluble at room temperature in anyaliphatic hydrocarbon having 5-12 carbon atoms per molecule may beregarded as asphaltene for the purpose of the present invention.

Asphaltenes may be isolated from other asphaltic constituents bypreferential precipitation. For example, asphalts may be introduced intoan aliphatic hydrocarbon precipitant (C alkanes) by several alternativemethods, dependent upon their physical characteristics. For example,hard asphalts (especially cracked or blown) having penetrations at 77 F.less than about 10 are preferably introduced by first dissolving them ina minimum amount,

of an aromatic hydrocarbon solvent. In order to minimize the effect ofthe aromatic solvent upon the precipitation of the asphaltene, it ispreferred that the proportion of solvent be restricted to between about0.5 and 2 volumes for each volume of the asphaltic residue. The aromaticsolvent is preferably one predominating in aromatic hydrocarbons havingless than 10 carbon atoms per molecule, of which benzene, toluene andxylene are suitable members. Softer asphalts may be dispersed byrefluxing in the presence of a limited proportion of the precipitatingaliphatic hydrocarbon, although the aromatic solvent may be used inaddition to or in place of the aliphatic medium. The maltene solutionand precipitated particles are separated by any suitable means,including filtration, centrifuging, sedimentation, decanting or similartreatment. Following separation of the asphaltene particles, they maythen be dissolved in an aromatic volatile solvent for use in themodification of microgel grease compositions. They may be added to suchcompositions under a variety of circumstances, such as by addition to anaqueous gel of the gelling agent or by dispersal in the lubricating oilprior to or subsequent to incorporation of the gelling agent in the oil.Preferably, asphaltenes-are incorporated in the oil subsequent toaddition of the colloidal gelling agent thereto and removal of anyvolatile solvents initially introduced together with the gelling agent.The table which follows gives an analysis of typical asphaltenes:

Asphaltene analysis It has been determined that asphaltenes arepolycyclic, contain numerous hetero atoms, particularly nitrogen, sulfurand oxygen, and usually contain between 1 and 13 hetero atoms, usually4-10, per asphaltene molecule on the average. The metallic content ofasphaltenes is in the order of 0.1-0.3%, the major constituents beingiron, vanadium, sodium and nickel. About A of the nitrogen atoms areweakly basic and only about 1% of the nitrogen atoms are strongly basic.Approximately of the sulfur groups exist as aliphatic or alicyclicsulfides, 1% as disulfides and 57% of the sulfur as thiophenes orpolythiophenes. In the average asphalt molecule, there are believed tobe about 150 carbon atoms, 18 hydroxyl groups, 3.4 nitrogen atoms, 1.5sulfur atoms and 2.1 oxygen atoms, although this analysis will dependupon the molecular weight selected as being nearest actuality. Moreover,there are understood to be about methyl radicals in the averageasphaltene molecule. The molecular weights of asphaltenes vary widelydependent upon the method by which the molecular Weight determination ismade. The table which follows shows that these vary all the way fromabout 2000 to 100,000 depending upon the method.

The asphaltenes may be oxidized either prior to or subsequent to theirseparation from other asphaltic components such as maltenes and thelike. Oxidation results in the conversion of maltenes to asphaltenes,and the further polymerization of asphaltenes. Oxidation may be carriedout by means well known in the asphalt art. For the most part, suchoperations are conducted by simply blowing the asphaltic body with airat an elevated temperature (450-550 F.) for an extended period ofbetween about 1-15 hours. The oxidation may be carried out in thepresence of oxidizing catalysts if desired, such as phosphoric acid,phosphorus pentoxide, ferric chloride, Friedel-Crafts catalyst, and thelike'although this is not an essential feature of this invention. Theisolated asphaltenes have been found to be especially sensitive tooxidation especially in the presence of ultraviolet light, such as sunlight.

The other constituents of the grease compositions of this invention arewell known in the art. They comprise lubricating oils which may bemineral lubricants, especially petroleum lubricating oils, as Well assynthetic lubricants, including esters, ethers, silicone fluids, andother well known materials. Specific lubricants include mineral oilbright stocks, methyl phenyl silicone fluids, dimethyl silicone fluids,polyphenyl ethers,-diesters of aliphatic dicarboxylic acids withmonohydric alcohols, such as bis- (2-ethylhexyl)sebacate, polyesters,such as'pentaerythritol esters of C aliphatic monohydric alcohols,complex esters formed between polybasic aliphatic acids and polyhydricalcohols, and other materials well known for their lubricatingproperties.

While these grease compositions are not intended to be restricted tolubrication in the presence of radiation, this constitutes one of theenvironments in which the properties of these greases show up togreatest advantage. For this purpose residual lubricating oils commonlyknown as bright stocks are preferred. The term bright stock is one whichis well recognized in the art of refining mineral oils. To obtain thedesired fraction, crude oils are usually subjected to distillation underordinary pressures in order to obtain a long residue comprising thefraction which does not distill under these conditions withoutsubstantial decomposition. The long residue is than subjected to steamdistillation, usually under a vacuum, or simply to vacuum distillation.Under these conditions, gas oil and waxy lubricant fractions distillover, leaving what is normally termed a short residue or a steam refinedstock, also known as cylinder stock. The steam refined stock is thendeasphalted (if an asphaltic crude is employed) and subjected todewaxing operations to remove microcrystalline or macrocrystallinewaxes. Following this, the oil is treated with a solvent for the purposeof reducing or removing the aromatic fractions. Clay contact treatmentor percolation may be employed to clean up the oil following any one orall of these separate operations. The raflinate which remains afterdeasphalting, dewaxing, extraction, and clay treatment is generallycalled bright stock.

The bright stocks suitable for use in the present compositions shouldhave the following ranges of properties:

TABLE I Properties of bright stocks Viscosity, S.U.S., at F., 1250,usually 1250-11,000,

preferably 1500-3500 Viscosity, S.U.S., at 210 F, 75, usually -325,preferably -250 Viscosity index 60, preferably 85-110 Aniline point 100,preferably 115 Flash, F., 475, preferably 500 Fire, F., 550, preferably600 Pour point, F., maximum 25, preferably lower than 15 Percentaromatics, 15, preferably 1 Percent naphthenes, 35

Percent paraifins, at least 60 The tables which follow give theproperties of typical bright stocks which are useful in the compositionsof this invention.

capable of maximum thickening of the lubricating oil as opposed toaerogels which are not suitable for grease formation. Aerogels arenormally prepared by forming TABLE II Examplesof typical bright stocksSUS Ring Analysis Aver- Vis- Average age cosity Rings 100 210 Index Aro-Naph- Paraf- Weight per matic thenes fins Mol Mid-Continent BrightStock:

Conventional o Extraction..-" 3,650 164 77 13 17 70 685 3.7 MildExtraction- 2,569 141 85 9 19 72 685 3.4 Deep Extraction. 2, 049 131 933 21 76 675 2.9 Perms lvania Bri id Stock 2,109 144 102 5 16 79 730 3.0CoastalBright Stock. 1, 251 85 63 4 35 61 515 3.4

TABLE III a hydrogel, displacing the water. therefrom with a relativelyvolatile miscible solvent such as acetone heating zd-Contment brz htstocks Speclficatlons for typlcalM g the organo gel so formed underpressure to a hlgh temd 25 perature and thereafter flashing the solventby release of Unfiltered F We pressure to form a dry powdery gel havinga highly ex- 7 O l 25 5 panded structure. Alternatively, the gels may bein- 81 Dark fg f; corporated into oil in the form of an organo gel fromPour izomtfir. ,maximum 10 10 ig which most or all of the water has beeneliminated and ,2 3 f ggfigf it; 322 610 30 thereafter stripping ed thevolatile solvent. Finally, the 8118210 F 0- 200-215 88 gels may betransferred into oil by the so-called direct Vlscoslty Index mmlmum' 909O transfer process wherein the hydrogel and oil are com- It will beunderstood from the above analyses that the source or treatment of aparticular mineral oil is not as important for the present purpose asthe final properties of the mineral oil constituent to be used in thesecompositions. For example, it is possible to vary theextent of solventextraction dependent upon the original aromatic content and therequirements of the specific use of the final product, as well as uponthe necessity or desirability of deasphalting, clay treating, acidtreating, and the like. Hence, it will be recognized that the presentinvention is predicated upon the use of a mineral oil fraction havingthe above defined ranges of properties and not upon the source ortreatment of such oil.

The two most important properties of a mineral oil suitable for thepresent use comprise the aromatic content and the viscositycharacteristics. The aromatic content has a large influence upon thesensitivity of the oil to thermal changes and the viscosity of the oilsdefines their suitability for their present purpose. Hence, the bestdefinition with respect to essential characteristics of mineral oilsuitable for the present compositions comprises those having a saturatemolecule hydrocarbon content between about 15-65% and having a viscosityof between about 1250 and about 11,000 SUS at 100 F. Having definedthese particular properties, the other properties such as flash, fire,aniline point, and viscosity index usually are largely dependent uponthem.

The gelling agents to be utilized in accordance with this inventioninclude particularly the clays having relatively high base-exchangecapacity, i.e., greater than milliequivalents per gram and preferablyabout 75-100 milliequivalents per gram. Bentonites, such as Wyomingbentonite and hectorite as well as other montmorillonites are preferred.In addition to the naturally occurring clays, other inorganic colloidsmay be utilized, such as silica, magnesia, magnesia-silica,silica-alumina and other amorphous colloidal gels. They may be used incombination with clays or may constitute the sole gelling agent. Meansare known for incorporating these classes of inorganic colloidal gels inlubricating oils for grease formation. Two of the favorite meanscomprise preparing the gels as aerogels which are low density gelsbined, preferably in the presence of the asphaltenes, thus, causingseparation of a major proportion of water from the gel, milling theremaining composition sufiiciently to disperse the gel throughout theoil and thereafter raising the temperature sufiiciently to eliminate thewater remaining by evaporation.

The greases ofthis invention are especially useful where thecompositions are to be subjected to ionizing radiation since theasphaltenes absorbed on the surface of the gelling agent .act in someundetermined manner to maintain the consistency and properties of thegrease. Thus, the greases are particularly useful for the lubrication ofbearings and other relatively moving metallic surfaces which are exposedin atomic piles, atomic reactors, atomic powered machinery, such as insubmarines and aircraft and for lubrication purposes generally whereradiation is encountered. However, this special virtue does notrestrictthe use of the grease to such locations since the greases are alsohighly satisfactory and effective for lubrication of bearings and othermetallic surfaces where greases are generally required.

Due to the relatively low cost of the stabilizing component, namely, theasphaltenes, the field of use of these greases is substantiallybroadened beyond that to which.

microgel greases can normally be applied. Hence, they are especiallyuseful for lubrication sites where high temperature or exposure to waterwill be encountered as well as in positions where ordinary operatingconditions prevail.

The following examples illustrate the advantages to be gained by the useof these greases: A grease composition was prepared by dispersinghectorite clay in a bright stock lubricating oil. The hectorite clay wasmodified by the presence of 60% by weight thereof of an amino amidehydrophobing agent. The grease contained 5% by weight of the clay. Asecond grease was prepared using the same bright stock lubricating oilto which was added a hectorite clay alcogel. After mixing, the alcoholwas evaporated by heating, leaving the clay dispersed throughout theoil, A xylene solution of blown asphaltene was then added to the mixtureand xylene evaporated, the components being milled thereafter to a.grease consistency. The grease contained 4% by weight of hectorite and3% by weight of blown asphaltenes. These two greases were subjected to ahigh temperature and high speed bearing test using the Standard FederalTest Meth od No. 331 which requires a temperature of 300 F. and 10,000r.p.m. The grease containing the amino amide ran for 562 hours until itfailed, while the grease containing blown asphaltenes ran 378 hoursuntil failure.

Other samples of the grease were then subjected to irradiation in a Vande Graafi accelerator until rads. of radiation had been absorbed. Theirradiated greases were then subjected to the same test conditions. Theirradiated grease containing the amino amide ran only 36 hours tofailure while the grease containing blown asphaltenes ran 148 hours tofailure. These comparative data illustrate the stabilizing effect 8f theasphaltene as compared with amino amides which are a usual type ofhydrophobing agent employed in microgel greases.

The blown asphaltenes employed in the above comparative tests wereobtained by air blowing a heavy crude lube residue having a 250 F.softening point and thereafter precipitating the asphalt with propaneand extracting the asphaltenes by precipitation in isopentane. Theasphaltenes had an average molecular weight (ebullioscopic) of 28,000.

The stability of greases to irradiation and the effect of unblownasphaltenes thereon was studied by determining the penetration of thegreases before and after irradiation thereof to the extent of 10 rads.radiation absorption. Sample A in the table below is the same claygrease modified with amino amide hydrophobing agent as was used in thetest described above. Sample B was the same as the second clay greasedescribed above containing asphaltenes. Table IV which follows shows thegreater stability of the greases containing the I claim as my invention:

1. A grease composition consisting essentially of a lubricating oilgelled to a grease consistency with a grease forming proportion of acolloidally dispersed clay, said clay having absorbed on the surfacesthereof a hydrophobing amount of asphaltenes.

2. A grease composition consisting essentially of a major proportion ofa mineral lubricating oil and a minor proportion sufficient to thickenthe oil to a grease consistency of a colloidally dispersed clay, saidclay bearing on the surfaces thereof a minor amount, sufficient toincrease the radiationand water-resistance of the grease, ofasphaltenes.

3. A grease composition consisting essentially of a major proportion ofa mineral lubricating oil and a minor proportion, sufficient to impart agrease consistency to the composition of a colloidally dispersedbentonetic clay, said gel bearing on the surfaces thereof a minoramount, sufficient to increase the radiationand waterresistance of thegrease, of oxidized asphaltenes.

4. A' grease composition consisting essentially of a major proportion ofa bright stock mineral oil gelled to a grease consistency with 1-15% byweight, based on the grease,of colloidally dispersed hectorite clay,said clay having adsorbed on the surfaces thereof 25-l00% by weight,based on the clay, of airblown asphaltenes.

5. A grease composition consisting essentially of a major proportion ofa polyphen-yl ether oil gelled to a grease consistency with 1-15 byweight of colloidally dispersed hectorite clay, said clay havingabsorbed on the surfaces thereof 25100% by weight, based on the clay, ofairblown asphaltenes.

References Cited in the file of this patent UNITED STATES PATENTS2,773,031 Tailleur Dec. 4, 1956 2,860,104 Peterson et al Nov. 11, 19582,885,360 Haden et al. May 5, 1959

1. A GREASE COMPOSITION CONSISTING ESSENTIALLY OF A LUBRICATING OILGELLED TO A GREASE CONSISTENCY WITH A GREASEFORMING PROPORTION OF ACOLLOIDALLY DISPERSED CLAY, SAID CLAY HAVING ABSORBED ON THE SURFACESTHEREOF A HYDROPHOBING AMOUNT OF ASPHALTENES.